Why does adaptive radiation lead to speciation

Population Genomics of different stages of adaptive radiation. David Alexander Marques Tel. Funding Swiss National Science Foundation grant no. Ecological speciation is the process by which reproductively isolated populations emerge as a consequence of divergent natural or ecologically-mediated sexual selection.

Most genomic studies of ecological speciation have investigated allopatric populations, making it difficult to infer reproductive isolation.

The few studies on sympatric ecotypes have focused on advanced stages of the speciation process after thousands of generations of divergence. As a consequence, we still do not know what genomic signatures of the early onset of ecological speciation look like. Here, we examined genomic differentiation among migratory lake and resident stream ecotypes of threespine stickleback reproducing in sympatry in one stream, and in parapatry in another stream. Importantly, these ecotypes started diverging less than years ago.

Consistent with incipient ecological speciation, we found significant genomic differentiation between ecotypes both in sympatry and parapatry. Of 19 islands of differentiation resisting gene flow in sympatry, all were also differentiated in parapatry and were thus likely driven by divergent selection among habitats. These islands clustered in quantitative trait loci controlling divergent traits among the ecotypes, many of them concentrated in one region with low to intermediate recombination.

Our findings suggest that adaptive genomic differentiation at many genetic loci can arise and persist in sympatry at the very early stage of ecotype divergence, and that the genomic architecture of adaptation may facilitate this. See DOI. See Institutional Repository. Marques, D. Speciation is a fundamental evolutionary process, the knowledge of which is crucial for understanding the origins of biodiversity.

Genomic approaches are an increasingly important aspect of this research field. We review current understanding of genome-wide effects of accumulating reproductive isolation and of genomic properties that influence the process of speciation. Building on this work, we identify emergent trends and gaps in our understanding, propose new approaches to more fully integrate genomics into speciation research, translate speciation theory into hypotheses that are testable using genomic tools and provide an integrative definition of the field of speciation genomics.

Seehausen, O. Ecological population genomics of constraints to adaptation and speciation in sympatry. Funding Swiss National Science Foundation, grant no. Genomics of ecological polymorphism in a marine fish group. Testing for ecological interactions between two salmonid radiations in the same lake. Carmela Doenz Tel. Jakob Brodersen Tel. Ecology and genetics of speciation in Pundamilia cichlids Identifying mechanisms of speciation has proven one of the most challenging problems in evolutionary biology, perhaps mainly for two reasons, speciation in sexually reproducing diploid organisms is not readily accessible to experimental approaches, and rarely to time series analyses.

Female mating preferences can influence both intraspecific sexual selection and interspecific reproductive isolation, and have therefore been proposed to play a central role in speciation. Here, we investigate experimentally in the African cichlid fish Pundamilia nyererei if differences in male coloration between three para-allopatric populations i.

Second, we investigate if female mating preferences are based on the same components of male coloration and go in the same direction when females choose among males of their own population, their own and other conspecific populations and a closely related para-allopatric sister-species, P. Mate-choice experiments revealed that females of the three populations mated species-assortatively, that populations varied in their extent of population-assortative mating and that females chose among males of their own population based on different male colours.

Females of different populations exerted directional intrapopulation sexual selection on different male colours, and these differences corresponded in two of the populations to the observed differences in male coloration between the populations. Our results suggest that differences in male coloration between populations of P. Selz, O. A critical step for speciation in the face of gene flow is the origination of reproductive isolation. The evolution of assortative mating greatly facilitates this process.

Assortative mating can be mediated by one or multiple cues across an array of sensory modalities. We here explore possible cues that may underlie female mate choice in a sympatric species pair of cichlid fish from Lake Victoria, Pundamilia pundamilia and Pundamilia nyererei. Previous studies identified species-specific female preferences for male coloration, but effects of other cues could not be ruled out.

Therefore, we assessed female choice in a series of experiments in which we manipulated visual color and chemical cues. We show that the visibility of differences in nuptial hue i. Such assortment mediated by a single cue may evolve relatively quickly, but could make reproductive isolation vulnerable to environmental changes. These findings confirm the important role of female mate choice for male nuptial hue in promoting the explosive speciation of African haplochromine cichlids.

This study compared Pundamilia nyererei and Pundamilia pundamilia males in routine metabolic rate R R and in the metabolic costs males pay during territorial interactions active metabolic rate, R A. Pundamilia nyererei and P. In contrast to expectation, however, P. This increased metabolic efficiency may be an adaptation to limit the metabolic cost that P. Thus, the divergence between the species in agonistic behaviour is correlated with metabolic differentiation.

Such concerted divergence in physiology and behaviour might be widespread in the dramatically diverse cichlid radiations in East African lakes and may be an important factor in the remarkably rapid speciation of these fishes.

The results did not support the hypothesis that higher metabolic rates caused a physiological cost to P. Dijkstra, P. Both inter- and intrasexual selection have been implicated in the origin and maintenance of species-rich taxa with diverse sexual traits. Simultaneous disruptive selection by female mate choice and male-male competition can, in theory, lead to speciation without geographical isolation if both act on the same male trait. Female mate choice can generate discontinuities in gene flow, while male-male competition can generate negative frequency-dependent selection stabilizing the male trait polymorphism.

We tested for genetic associations among female mating preference, male aggression bias and male coloration in the Lake Victoria cichlid Pundamilia. We crossed females from a phenotypically variable population with males from both extreme ends of the phenotype distribution in the same population blue or red.

Male offspring of a red sire were significantly redder than males of a blue sire, indicating that intra-population variation in male coloration is heritable. We tested mating preferences of female offspring and aggression biases of male offspring using binary choice tests. There was no evidence for associations at the family level between female mating preferences and coloration of sires, but dam identity had a significant effect on female mate preference. Sons of the red sire directed significantly more aggression to red than blue males, whereas sons of the blue sire did not show any bias.

There was a positive correlation among individuals between male aggression bias and body coloration, possibly due to pleiotropy or physical linkage, which could facilitate the maintenance of color polymorphism. Adaptive radiations are an important source of biodiversity and are often characterized by many speciation events in very short succession. It has been proposed that the high speciation rates in these radiations may be fuelled by novel genetic combinations produced in episodes of hybridization among the young species.

The role of such hybridization events in the evolutionary history of a group can be investigated by comparing the genealogical relationships inferred from different subsets of loci, but such studies have thus far often been hampered by shallow genetic divergences, especially in young adaptive radiations, and the lack of genome-scale molecular data. Here, we use a genome-wide sampling of SNPs identified within restriction site—associated DNA RAD tags to investigate the genomic consistency of patterns of shared ancestry and adaptive divergence among five sympatric cichlid species of two genera, Pundamilia and Mbipia , which form part of the massive adaptive radiation of cichlids in the East African Lake Victoria.

Species pairs differ along several axes: male nuptial colouration, feeding ecology, depth distribution, as well as the morphological traits that distinguish the two genera and more subtle morphological differences. Using outlier scan approaches, we identify signals of divergent selection between all species pairs with a number of loci showing parallel patterns in replicated contrasts either between genera or between male colour types.

We then create SNP subsets that we expect to be characterized to different extents by selection history and neutral processes and describe phylogenetic and population genetic patterns across these subsets.

These analyses reveal very different evolutionary histories for different regions of the genome. To explain these results, we propose at least two intergeneric hybridization events between Mbipia spp. Keller, I. Environmental variation in signalling conditions affects animal communication traits, with possible consequences for sexual selection and reproductive isolation. Because adaptive radiations produce diversification through ecological specialization, they are essential for understanding how ecological forces can drive evolutionary diversification and shape the way species interact with their environments.

Among vertebrates, African cichlid fishes are justly recognized as stunning examples of adaptive radiation. Most remarkably, each of the species flocks of the Rift Valley lakes Victoria, Malawi and Tanganyika independently diversified into hundreds of species with remarkable ecological and behavioral specializations. Unfortunately, research focus on African lacustrine cichlids has left their riverine counterparts virtually unstudied from an evolutionary point of view.

The fundamental question of whether riverine cichlids can undergo adaptive radiation has not been extensively addressed. Because cichlids are one of the three most-diverse families of Neotropical freshwater fishes along with Characidae and Loricariidae , they are ideal models for studying the incomparable fish diversity of the Neotropics. Neotropical cichlids include approximately 60 genera and more than species including many still undescribed.

Ecological variation in Neotropical cichlids includes fish predators, rapids-dwelling invertebrate feeders, insect eaters with disc-like bodies, detritus eaters, and a variety of groups that extract invertebrates from the substrate by filtering sand or mud using their pharynx.

He is exploring remote areas of South and Central America to document and describe new species of cichlids, and to gather data to answer questions such as: Which groups of American cichlids fulfill the requisites for Adaptive Radiation?

What are the relationships among species within each of these radiations? Variants from all phenotypic extremes of the distribution curve may be able to find conditions that favor their particular adaptations.

Consequently, they spread out, discover a niche that suits them, and exploit their new capacity for growth and reproduction. Rapid isolation and speciation lead to proliferation and new species as each new gene pool diverges and separates. On phylogenetic diagrams, adaptive radiation resembles a fan-shaped, branching pattern because a multitude of new species arise in a short time and quickly diverge.

Eventually, however, these new species will begin to encounter one another again and start living closer and closer together. Inevitably, there will be competition for resources such as food, shelter, and nesting sites. However, the niche rule states that only one of a group of closely related species may occupy the same niche in a given habitat.

Competition between species 1 and 2 ensues, placing pressure on both groups to adapt to separate niches, further distinguishing them from each other and the parent species. As this happens many times in a given habitat, several new species may be formed from a single parent species in a relatively short period of time. Darwin's finches are an excellent example of adaptive radiation. SparkTeach Teacher's Handbook.